Sediment transport process in mountain streams has been studied chiefly in the development of theoretical as well as experimental bed load equations. Difficulties associated with field observation have been a major obstacle in testing and applying bed load equations properly. Direct sediment sampling is often impossible ; and its effective is limited due to its durability even if it is applicable. Attempts have been made to utilize more indirect but stable monitoring methods (hereafter “indirect method") in recently years such as a hydrophone sediment discharge measuring system (hereafter “hydrophone system"). Hydrophone systems count the times that bed load sediments strike the acoustic sensor of the system (hereafter “pulses") upon proper electric amplification. Early observation brought light on small to medium discharge non-equilibrium sediment transport phenomena which have not been adequately studied either theoretically or experimentally. Non-equilibrium states are influenced by many hydro-sediment factors, among which flow discharge is not always dominant. Therefore, sediment discharge as a functional form needs to be regarded as dependent on multiple variables. Expanding bed load equations and building ones from many primary hydro-sediment factors at one time seem to be beyond our reach. Thus, a step-wise approach is taken by introducing and adding to flow discharge an intermediary and secondary hydro-sediment factor called “sediment-related quantity," which is observed by indirect methods.In this study, hydrophone systems have been installed in 100 and 200 km²-scale river basins in order to observe hydrophone pulses that are used as sediment-related quantity. Sediment transport, water flow, and acoustic phenomenon are mutually intercorrelated. The phenomena were described by each corresponding observational variables, whose correlations were analyzed statistically. Hydrophone pulses have correlation with and are dependent upon both bed load discharge and flow discharge. Therefore, pulses alone can not provide suitable estimates of sediment discharge. In order to search analytical estimation equations of bed load, therefore, pulses and flow discharges were combined as an initial step. Additive forms both with and without interaction terms, and multiplicative forms were introduced and calibrated for the observation. Each bed load analytical estimation method was statistically assessed. The best method was a linear additive form with no interactive term. The introduction of sediment-related quantities facilitates us to construct a viable analytical estimation method of non-equilibrium sediment discharge. Its own dependency on other hydro-sediment factors needs to be examined for further physical understanding of the sediment discharge observation. Indirect method with the suggested forms of analytical estimation equations, with due care for its insufficient physical understanding,seems to be applicable for further development to analyze bed load discharge consecutively in the scale of full river section.

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Tanakamiyama locates surrounding Seta at Ohtsu city and its had been completely devastated about 120 years ago because of over logging for firewood and lumber. In Edo period, a lot of sediment flowed out, to rise riverbed downstream and to cause flood frequently. Intense hillside works ; terracing and planting have been implemented for last 120 years. The area are covered green almost completely today. Erosion rate have been observed last 30 years in this area. We estimated sediment production in old days, since 120 years ago to the present from the recent 30 years observation data. And we calculated changes of sedimentation from 120 years ago to the present using numerical calculation method. The results shows as a below ; (1) Devastated area in the Daido river basin has been reduced from 19 km² to 1 km² during 120 years. In the Tanakamiyama district, devastated area has been reduced from 9 km² to 0.89 km², too. (2) The amount of sediment outflow from devastated area, is from 1,000 to 10,000 m³/km²/year, has been reduced to 100 m³/km²/year 10 years elapsed after implemented hillside works. (3) When vegetation coverage rate will recover to 60 percent, the amount of sediment outflow less than 1 m³/km²/year. (4) To construct the hillside work, the amount of sediment outflow has been reduced to 60 present after 120 years at the downstream end section of Uji river. (5)Tendency of the amount of sediment outflow after implemented hillside works is a high to decrease early close to sediment yield area. But the downstream area is the delay at the onset time, the less impact.

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Volumetric changes in volcanic mudflow occurred in 1926 at Mt. Tokachi was successfully estimated using both sediment remnants in the investigation area and historical archives. The aim of this study is to clarify the flow and sedimentation process of the 1926 mudflow. We carried out the equilibrium experiment to confirm the separation of the fluid and solid phase under the similar condition of 1926 mudflow deposition. Moreover, we analyzed the found document that indicates the detail distribution and the thickness in particular point of the mudflow just after mudflow occurrence. Cumulative volume of mudflow deposit in the flooding area located in lower half reach of the Furano river was estimated at 3,200,000 m³. Discharge yielded from source area was calculated at 6,500,000 m³ including original collapse of crater, melting water from the foot slope and erosion sediment along the river course, and has grown up at 6,900,000 m³ with plus 400,000 m³ from transport area. At last, the 3,200,000 m³ of mudflow deposit was deposited in the flooding area and the residual mudflow estimated to flashed over downstream. Knowledge developed by the calculation of mudflow volume from source to flooding area allowed drawing the longitudinal change in mudflow volume.

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Slope failures which caused disasters in 2004 and 2005 are investigated taking note of the travel distance, fluidized condition, influence of structures. In the investigated cases, most of failed soil was traveled under 5 m (81.6%),deposited near the end of slope (85.5%). In the cases without structure, 41% of the failed soil mass was keeping the shape. Therefore, most of the failed soil mass should be not fluidized. In the cases with receiving type wall structures,receiving effect was recognizable for slope failure traveling under 10 m, but not for over 10 m. Therefore receiving type wall structure should have limit of receiving large or fluidized failed soil. In most of the studies on the movement of failed soil mass, condition of fluidization and the movement of fluidized soil were subjected. The movement mechanism of not fluidized soil mass caused by slope failure should be studied hereafter.

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Various bedload measurement techniques have been developed so far and they has been examined. For example, as the indirect measurement technique with sensor, there is hydrophone. Many studies are performed about it, but various problems are pointed out. Therefore, it cannot be said that the indirect technique about bedload measurement is established. And then, we tried bedload measurement with a radar. Because we placed this study with fundamental experiment, we studied it in standing water not flowing water. We installed antennas in the water tank base. And we moved various targets and examined the signal strength change of radar. It was recognized that the radar caught flowing sand and difference of relative permittivity change from the result of the experiment. Therefore, we suggested that bedload measurement with radar was possible.

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It is very important to know the distribution of slope failures quickly just after the big earthquake against the additional sediment related disaster. Generally, the sabo facilities damage check after the earthquake is carried out when the seismic intensity scale is exceeded 4 by JMA were observed. We evaluated the relationship between the distributions of seismic intensity and the hazard area concerned with slope failures distribution in the case as followed as ; The Mid Niigata prefecture earthquake in 2004, The Noto Hanto earthquake and the Niigataken chuetsu earthquake in 2007. Following our study indicated that slope failures appeared in more than seismic intensity scale 5 lower and the tendency of the serious disaster increasing when the seismic intensity is more than 5 upper. It suggested that the slope failure check might be carrying out quickly when the seismic intensity observed more than 5 upper.

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